1. Field of the Invention
The present invention relates to a cylinder injection type fuel injection valve to be used in a cylinder injection type internal combustion engine (four-cycle engine or two-cycle engine) that gives swirling energy to fuel streams by a swirling device and injects the fuel from a fuel injection nozzle directly into a combustion chamber, in particular a fuel injection valve appropriate to fuel injection with a small angle of spray from the injection nozzle.
2. Discussion of Background
Heretofore, there has been an internal combustion engine wherein premixed combustion is carried out at a high output and stratified combustion is carried out at a low output, and that the premixed combustion and the stratified combustion are switched in accordance with the operational conditions of the engine as disclosed in WO96-36808. Such an internal combustion engine can optimize the shape of a combustion chamber, an air streaming method, the position of a fuel injection valve, characteristics of the spray, the position of an ignition plug and other factors in order to meet incompatible requirements of improvement in output and improvement in mileage.
However, when such an internal combustion engine is used for, e.g., an automobile, the optimization of these factors can not be realized in all cases since there are various limitations based on the system or the specifications of the engine, parts for induction and exhaust systems, the layout of parts for a fuel system and the appearance of the vehicle.
Unless there is adopted a method wherein improvement in output is compatible with improvement in mileage with existing techniques and facilities utilized, the production cost is raised, making the business unprofitable.
Under the circumstances, one of the most important technical issues is that premixed combustion and stratified combustion are compatible. In order to make the two combustion concepts compatible, the shape of a combustion chamber, an air streaming method, the position of a fuel injection valve, the characteristics of spray, the position of an ignition plug become relevant as stated earlier. It is fundamental that homogenous mixture is created by diffused spray in premixed combustion and that converged spray is collected in the vicinity of an ignition plug in stratified combustion.
Various kinds of investigations have been conducted about the research on new peripheral parts for a fuel system, system concepts for a fuel system or a combustion system, control methods and other issues in order to realize the technical issue stated earlier while minimizing the increase in cost with existing techniques, facilities and parts utilized.
In order to explain the basic structure of such a cylinder injection type fuel injection valve, the fuel injection valve that has been disclosed in JP-A-1047208 will be explained as a conventional fuel injection valve.
In FIG. 6 is shown a cross-sectional side view of the entire structure of the cylinder injection type fuel injection valve 1 disclosed in the publication. The cylinder injection type fuel injection valve 1 comprises a main housing 2, and a valve unit 3 fixed to an end of the main housing 2 by, e.g., caulking and covered by a holder 35. The main housing 2 has the other end connected to a fuel supply pipe 4, from which fuel is supplied, at a high pressure, into the cylinder injection type fuel injection valve 1 through a fuel filter 57. The cylinder injection type fuel injection valve 1 has a leading portion inserted into an inserting port 6 of a cylinder head 5 in an internal combustion engine and sealed by, e.g., a wave washer 60 or a similar member.
The valve unit 3 includes a valve body 9 formed in a stepped hollow cylindrical shape so as to have a small diameter of cylindrical portion 7 and a large diameter of cylindrical portion 8, a valve seat 11 fixed to a leading edge of a central hole in the valve body 9 and having a fuel injection nozzle 10 formed therein, a needle valve 12 as a valve-closure member to be moved away from and toward the valve seat 11 by a solenoid unit 50 stated later on to open and close the fuel injection nozzle 10, a swirler 13 for guiding the needle valve 12 in an axial direction and for radially and inwardly giving swirling movement to the fuel before the fuel enters the injection nozzle 10. The valve body 9 of the valve unit 3 and the main housing 2 provide the cylinder injection type fuel injection valve 1 with a total housing.
The main housing 2 includes a first housing 30 having a flange 30a for mounting the cylinder injection type fuel injection valve 1 to the cylinder head 5, and a second housing 40 with the solenoid unit 50 mounted thereon. The solenoid unit 50 includes a bobbin 52 with a coil 51 wound thereon and a core 53 provided at an inner peripheral portion of the bobbin 52. The coil 51 is connected to a terminal 56. The core 53 is formed in a hollow cylinder shape to provide a fuel passage therein. The core 53 has a spring 55 provided between a sleeve 54 and the needle valve 12 in the hollow portion thereof.
The needle valve 12 has an end remote from the valve seat 11 provided with a movable armature 31 so as to confront a leading edge of the core 53. The needle valve 12 has an intermediate portion thereof provided with a guide 12a for slidably guiding the needle valve 12 along an inner peripheral surface of the valve unit 9, and a needle flange 12b in contact with a spacer 32 provided in the first housing 30.
In FIG. 7 is shown a front view of the swirler 13 as viewed from the side of the valve seat 11. In FIGS. 8 and 9 are shown an enlarged cross-sectional side view and an exploded perspective view of the valve seat of the valve unit 3 and its surroundings. As shown in these Figures, the swirler 13 of the valve unit 3 is a hollow member formed in a substantially cylindrical shape, which has a central hole 15 formed therein so as to surround the needle valve 12 as the valve-closure member at the center and to slidably support the needle valve in the axial direction. The swirler includes a first end surface 16 and a second end surface 17. When the swirler is assembled into the valve unit 3, the first end surface contacts the valve seat 12 and the second end surface is located on the side remote from the valve seat 11. The swirler has an outer circumferential surface 19 extended between both end surfaces so as to partly contact the inner peripheral surface 18 of the valve body 9 as a part of the hollow total housing.
The second end surface 17 of the swirler 13 has peripheral portions contacted with and supported by a shoulder 20 provided on the inner peripheral surface 18 of the valve body 9. The second end surface has grooved passages 21 radially formed thereon to flow the fuel from an inner periphery to an outer periphery of the second end surface.
The outer circumferential surface 19 of the swirler 13 has a plurality of flat surfaces formed thereon so as to be separated one another at equal intervals in the circumferential direction and to extend in the axial direction. Thus, a plurality of outer peripheral surface portions 19a that contact the inner peripheral surface 18 of the valve body 9 to define the position of the swirler 13 to the valve body 9, and flow passage portions 19b that are flat surfaces provided between adjacent outer peripheral surface portions to form axial passages 22 for the fuel between the inner peripheral surface 18 and the flat surfaces are provided on the outer circumferential surface 19.
On the first end surface 16 as an axial end surface of the swirler 13 confronting the valve seat 11, an inner annular groove 24 is provided at an inner periphery close to the central hole 15 of the first end surface 16 so as to have a certain width, and swirling grooves 25 are provided so that one end of each of the swirling grooves is connected to a flow passage portion 19b on the outer circumferential surface 19 and that each of the swirling grooves extends in an almost radially inward direction to have the other end connected to the inner annular grove 24 in a tangential direction.
Next, the operation of the cylinder injection type fuel injection valve will be explained. When the coil 51 of the solenoid unit 50 is energized through the terminal 56 from the external, magnetic flux is generated in the magnetic circuit formed by the movable armature 31, the core 53 and the main housing 2 to attract the movable armature 31 toward the core 53 against the elastic force of the spring 55. As a result, the needle valve 12, which is integral with the movable armature 31, is moved in the right direction in FIG. 6 by a certain stroke until the needle flange 12b contacts the spacer 32. The needle valve 12 is guided and supported on the inner peripheral surface of the valve body 9 by the guide 12a.
When the leading edge of the needle valve 12 gets away from the valve seat 11 to provide a gap, the fuel, which is introduced from the fuel supply pipe 4 at a high pressure, flows into the axial passages 22 on the outer circumferential surface 19 from the passage between the valve body 9 and the needle valve 12 through the grooved passages 21 in the second end surface 17 of the swirler 13. Then, the fuel flows into the swirling grooves 25 in the first end surface 16 of the swirler 13 and is directed to a radially inward direction. After that, the fuel flows tangentially into the inner annular groove 24 in the first end surface 16, enters the injection nozzle 10 in the valve seat 11 as swirling streams, and is sprayed through the outlet at the leading end of the nozzle. In FIG. 9, reference numeral 11a designates a tapered surface provided on the valve seat, reference numeral 12c designates a rounded surface of the valve-closure member, and an arrow C designates the flow direction of the fuel.
The present invention provides a fuel injection valve appropriate to an engine wherein the combustion concept is optimized when the fuel injection valve has a relatively small angle of spray (not greater than 50.degree.), or when the spray density is symmetrical with respect to the spray axis though there is little influence of a degree of hollow cone (a degree of solidity) of the spray. In order to decrease the angle of spray in a conventional swirler 13 shown in FIG. 10(a) as an enlarged view of the essential portion, a change in design, such as an increase in the cross-sectional area of the swirling grooves 25 as shown in FIG. 10(b), is required. However, when the swirling grooves have a width W.sub.1 enlarged, adjoining swirling grooves interfere each other in swirlers with the grooves formed at the number of, e.g., four of six, an effective length L.sub.1 thereof is shortened to L.sub.2. Thus, the fuel streams in the respective swirling grooves 25 flow into the inner annular groove 24 and join together without being stabilized, creating a problem in that it is difficult to equalize the swirling streams.
In addition, the inner annular groove has an effective annular diameter extended from D.sub.1 to D.sub.2 to increase the amount of non-swirling fuel at an initial spraying stage, having adverse effect on the combustion in some cases. In other words, a portion of the fuel (the volume from a location upstream the swirling grooves of the swirler to a location upstream the valve seat=non-swirling volume, the portion indicated by "B" in FIG. 11) is sprayed without being subjected to swirling movement at an initial spray stage, and the particle size in that portion is greater since almost no swirling movement is given to that portion. When the groove depth d of the swirling grooves is relatively smaller than the width of the swirling grooves, it is presumed that almost no swirling movement is given because of the provision of such a flow pattern to extrude almost the entire amount of the non-swirling volume at the initial spray stage.
The provision of the grooves at a number smaller than four is not appropriate since the provision of the grooves at such a number can not equalize the swirling streams inherently.
Next, a case wherein the groove depth is enlarged to increase the cross-sectional area of each of the grooves irrespectively of the width of the swirling grooves will be considered.
Since the valve-closure member normally has an outer surface portion confronting the outlets of the grooves formed in an almost rounded shape or a tapered shape even in a totally closed state as shown in FIG. 11, the outer surface portion provides an aid to give axial components to the swirling streams so as to helically flow out the streams. For example, the effect offered by the outer surface portion is great when the angle of spray is from about 50.degree. to about 80.degree.. When the angle of spray is great, the helical angle (the angle from a plane perpendicular to the axis of the valve-closure member) of helical streams is small, which means that there are an enough time and enough room to equalize the swirling components provided in a number corresponding to the number of the grooves.
On the other hand, when the value required for the angle of spray is small, it is required to make design so as to decrease swirling forces. When the outer surface portions of the valve-closure member confronting the outlet of the grooves is formed in a rounded shape or tapered shape since the helical angle is great, the fuel streams are flowed out without having the swirling components equalized. As a result, the conical shape of the spray is not uniform though the angle of spray is small, or the spray is formed in a polygonal shape to correspond the number of the grooves as shown in FIG. 12(a). In FIG. 12(b) is shown the ideally shape of the spray.
If the spray is formed in such a way, it is required not only to define the position of the swirler in the circumferential direction in the production of a fuel injection valve but also to accurately define the orientation (the position) of the swirler in the circumferential direction during mounting the fuel injection valve to an engine. Otherwise, variations in the combustion state of the respective cylinders or variations in the combustion state of respective engines are caused, which is extremely inconvenient.